Phoebe 土卫九(中英)

Phoebe is the outermost¹ of Saturn²'s known satellites. Phoebe is almost 4 times more distant from Saturn than its nearest neighbor (Iapetus).

　　orbit:    12,952,000 km from Saturn

　　diameter: 220 km

　　mass:     4.0e18 kg

　　Phoebe is the daughter of Uranus³ and Gaia; grandmother of Apollo and Artemis.

　　Discovered by Pickering in 1898.

　　On June 11, 2004 Cassini passed close to Phoebe on its way into the Saturn system, giving us our first real look at it since Voyager and at much higher resolution.

　　Most of Saturn's moons are bright but Phoebe's albedo is very low (.05), as dark as lampblack.

　　All of Saturn's moons except for Phoebe and Iapetus orbit very nearly in the plane of Saturn's equator. Phoebe's orbit is inclined almost 175° (its north pole is in the opposite direction to Saturn's).

　　Phoebe's eccentric, retrograde orbit and unusual albedo indicates that it may be a captured comet or Kuiper Belt object. Data from Cassini's 2004 flyby reinforces this idea with the detection of CO2 trapped within its rocks. This rules out the earlier idea that it might have been a captured asteroid⁴. It appears that Phoebe is chemically similar to Pluto⁵ and Triton. It is probably very similar to the chemical composition of the outer solar system at the very beginning.

　　Phoebe is also unusual in that it does not rotate synchronously⁶ as do all the other moons of Saturn except Hyperion.

　　Material knocked off of Phoebe's surface by microscopic⁷ meteor impacts may be responsible for the dark surfaces of Hyperion and the leading hemisphere of Iapetus.

　　Phoebe 是土星已知卫星中最外层一颗，几乎是其近邻卫星（土卫八）到土星距离的4倍。

　　公转轨道：距土星 12,952,000 千米

　　卫星直径：220 千米

　　质量：4.0e18 千克

　　福柏(Artemis)是狩猎与月亮女神，阿波罗的同胞妹妹。

　　它由Pickering于1898年发现。

　　大多数土星的卫星是明亮的，但是土卫九的反照率只有0.05，像煤烟一样暗。

　　除了土卫九与土卫八，所有的土星卫星公转面与土星赤道面一致。土卫九公转倾斜角近175度（它的北极与土星的正相反）。

　　土卫九的偏心的，逆向的公转轨道和不寻常的反照率说明它可能是一颗被捕捉的小行星或是Kuiper带中的物体。

　　土卫九的不寻常还表现在自转非同步，与其他土星卫星除土卫七外不同。

　　由于细微的流星体撞击，土卫九上掉落的物质可能与土卫七表面和土卫八逆公转半球的黑暗有关。